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What the label lists and what reports show

Peginterferon alfa 2a side effects

Peginterferon alfa 2a's FDA label: “The most common life-threatening or fatal events induced or aggravated by PEGASYS and ribavirin include depression, suicide, relapse of drug abuse/overdose, and bacterial infections, each occurring at a frequency of less than 1%.” FAERS holds 53,742 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is fatigue (9,258 reports).

  • No generic listed
  • Boxed warning

Check it at the source: the peginterferon alfa 2a FDA label on DailyMed (effective September 2, 2026); the FDA FAERS public dashboard.

What does the patient leaflet say about side effects?

From the patient leaflet: What are the possible side effects of PEGASYS?

PEGASYS can cause serious side effects including: See " What is the most important information I should know about PEGASYS? " Blood problems.PEGASYS can affect your bone marrow and cause low red blood cell, low white blood cell and low platelet counts. These blood counts may fall to dangerously low levels. If your blood cell counts become very low, you can get anemia, infections or have problems with bleeding and bruising. Thyroid problems. Symptoms of thyroid changes include feeling cold or hot all the time, a change in your weight, and changes to your skin, trouble concentrating. Blood sugar problems. PEGASYS may cause low blood sugar (hypoglycemia), high blood sugar (hyperglycemia) or diabetes. If you have high blood sugar or diabetes before starting PEGASYS, talk to your healthcare provider before you take PEGASYS. […]

Source: FDA drug label, pharmaand GmbH, effective September 2, 2026 (SPL set d9290e5b-6d40-2318-e053-2995a90a9916), via openFDA; the full label on DailyMed

What does the label list?

From the label: adverse reactions

The most common life-threatening or fatal events induced or aggravated by PEGASYS and ribavirin include depression, suicide, relapse of drug abuse/overdose, and bacterial infections, each occurring at a frequency of less than 1%.

Table 7 Adverse Reactions Occurring in Greater Than or Equal to 5% of Subjects in Chronic Hepatitis C Clinical Trials (Pooled Studies 1, 2, 3, and Study 4)

Body SystemPEGASYS 180 mcg 48 week Pooled studies 1, 2, and 3 N=559 %ROFERON-A Either 3 MIU An induction dose of 6 million international units (MIU) three… N=554 %PEGASYS 180 mcg + 1000 mg or 1200 mg Ribavirin 48 week Study 4 N=451 %Intron ® A + 1000 mg or 1200 mg Rebetol ® 48 week N=443 %
Injection site reaction22182316
Hypothyroidism3245
Fatigue/Asthenia56576568
Pyrexia37414155
Rigors35442537
Pain1112109
Nausea/Vomiting24332529
Diarrhea16161110
Abdominal pain151589
Dry mouth6347
Dyspepsia<1165
Lymphopenia351412
Anemia211111
Neutropenia218278
Thrombocytopenia525<1
Anorexia17172426
Weight decrease431010
Myalgia37384049
Arthralgia28292223
Back pain91055
Headache54584349
Dizziness (excluding vertigo)16121414
Memory impairment5465
Overall1061210
Irritability/Anxiety/Nervousness19223338

Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.

From the label: adverse reactions, continued

In clinical trials, a broad variety of serious adverse reactions were observed in 1,010 subjects who received PEGASYS at doses of 180 mcg for 48 weeks, alone or in combination with ribavirin [see Boxed Warning and Warnings and Precautions (5) ]. The most common life-threatening or fatal events induced or aggravated by PEGASYS and ribavirin include depression, suicide, relapse of drug abuse/overdose, and bacterial infections, each occurring at a frequency of less than 1%. Hepatic decompensation occurred in 2% (10/574) of CHC/HIV subjects [see Warnings and Precautions (5.9) ]. Adult subjects: The most common adverse reactions (incidence greater than 40%) are fatigue/asthenia, pyrexia, myalgia, and headache ( 6.1 ) Pediatric subjects: The most common adverse reactions are similar to those seen in adults ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact pharma& agent at 1-888-814-7734 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying and controlled conditions, adverse reaction rates observed in clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug, and may not reflect the rates observed in clinical practice. …

Source: FDA drug label, pharmaand GmbH, effective September 2, 2026 (SPL set d9290e5b-6d40-2318-e053-2995a90a9916), via openFDA; the full label on DailyMed

What do FAERS reports show?

53,742 reports list peginterferon alfa 2a among the medicines taken, each a report of something that happened, not proof the medicine caused it; 1,798 are coded as a death and 9,496 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 24 reactions below, 17 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.

Reports received each year

The 25 most reported reactions

  • Fatigue (named in the label)9,258
  • Nausea (named in the label)7,164
  • Anaemia (named in the label)6,630
  • Rash (named in the label)4,877
  • Headache (named in the label)4,455
  • White Blood Cell Count Decreased4,229
  • Pruritus (named in the label)4,225
  • Pyrexia (named in the label)3,475
  • Diarrhoea (named in the label)3,384
  • Vomiting (named in the label)3,336
  • Asthenia (named in the label)3,150
  • Insomnia (named in the label)3,079
  • Dyspnoea (named in the label)3,051
  • Decreased Appetite (named in the label)2,918
  • Influenza Like Illness (named in the label)2,738
  • Weight Decreased2,659
  • Dizziness (named in the label)2,625
  • Platelet Count Decreased2,578
  • Depression2,552
  • Pain2,543
  • Chills (named in the label)2,192
  • Haemoglobin Decreased2,042
  • Anorectal Discomfort1,845
  • Drug Ineffective (a use or a product term, not a reaction)1,744
  • Alopecia (named in the label)1,675

Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms

What next?

Peginterferon alfa 2a: the full record
label, generics, price, shortages, recalls
Side effects hub
the most reported medicines and reactions